In many systems, important data may need to be saved upon an interruption of power in order to resume normal system operation when power is restored. In some systems, saving this information requires circuitry having a large backup power source (e.g., a battery and/or large capacitor) having enough stored energy to keep the circuitry operational while data is saved during a shutdown process.
Because non-volatile memory (memory that can retain data without a power connection) is generally slower and less robust for handling repeated in-process data storage, circuits typically include volatile memory (e.g., RAM) for saving data during real-time operations (e.g., tracking in memory the position of a moving object). On the other hand, non-volatile memory such as an electrically erasable read only memory (EEPROM) is often used for storing data when a continuous power source isn't available and/or data needs to be saved and restored when a system powers down and restarts. In some systems, volatile memory may include memory registers which operate to store and/or update the continuous stream of data.
A vehicular electronic steering system is an example of a system which continuously updates memory in order to track and update the position of a steering wheel. Circuitry used in some electronic steering systems includes a so-called “turns count register” that is used to keep count of a number of wheel turns beyond 360 degrees e.g. the number of turns made by a gear tooth. The angular change for which the register is incremented/decremented is programmable.
The turns count register circuitry receives power from a power supply. If the power supply fails or is otherwise disconnected from the circuitry, the information in the turns counter register may be lost.
To prevent loss of information from the turns counter register, the part may also comprise a non-volatile memory (i.e. a memory not affected by the loss of power such as an EEPROM) in which information from the turns counter register may be stored in response to power loss. To transfer data from the part to the non-volatile memory, a control pulse having a predetermined voltage (e.g. 19 volts) must be applied to the EEPROM for a predetermined amount of time (e.g. about 10 milliseconds). One way to ensure that such a pulse is provided in the event of a loss of power from power supply is to have an external capacitor of considerable size (e.g. having a capacitance in the microFarad range) which can power a charge-pump (and associated control circuitry) and the non-volatile memory (e.g. an EEPROM) for an amount of time sufficient for the pulse to be applied.
Such large external capacitors take up critical space where demands for ever smaller circuitry, for which more sensitive data is becoming needed for storage and during a power interruption as such systems become more complex and data intensive. Thus, circuitry for saving larger amounts of data using less power is desired.